How auto updated for iOS app works on the App Store?

We have released an iOS app update (4.0), this update introduced a critical bug in our production App, to fix that bug, we released a host fix (4.0.1), hot fixed and approved within a day.

Problem is:

Most of our users are still auto-updating to 4.0 (older version) while the latest version 4.0.1 is available at the app store; is it an expected behavior?

In the case of manual updates, users are getting the latest version 4.0.1